1. Field of the Invention
The field of the invention is the interrogation of radio frequency identification (RFID) transponders. More specifically, the field of the invention is interrogating a known number of RFID transponders associated with items placed on a shipping pallet while such shipping pallet is rotated during a process of applying a shipping membrane to stabilize the items of the shipping pallet or while an RFID reader is rotated substantially about the items.
2. Description of Related Art
Item tracking and identification has advanced with the development of machine-readable indicia such as barcodes and machine-readable devices such as RFID transponders. RFID transponders are beginning to garner more favor as they are capable of providing more information than a barcode and as their costs decrease. Information about an item that may be included in an RFID transponder can include item identification information, stock-keeping information, ownership information, shipping information, etc. In manufacturing, warehousing and shipping environments, items may be associated with RFID transponders to track them as well as to provide information about the model or serial number, location, cost, shipper, recipient, recipient's address, etc. In many instances, items that are tagged (i.e., associated) with an RFID transponder will have their RFID transponder interrogated numerous times as the item makes it way through the manufacturing, warehousing or shipping processes. Essentially, any process that uses automatic identification technologies requires a medium to store information that will subsequently be retrieved by various applications for processing. Such a medium is provided by RFID transponders. Transponders come in a variety of sizes and designs, and there are numerous types, each tailored to meet different application requirements.
RFID transponders (a/k/a “tags”) have at least two components, an integrated circuit (IC) chip and an antenna. The chip and antenna can be laminated on plastic cards, encapsulated in protective housings, embedded in label stock, or produced in numerous other ways and forms. The amount of information that may be stored in a RFID tag varies, some tags are able to store significant amounts of information while others are designed to record a single identifier, much like a barcode. Tags also differ in their power sources and how they send/receive information to/from RFID readers.
RFID tags can be classified as either active or passive. This classification describes the tag's power source and how the tag sends information to readers. Active tags have an internal transmitter powered by an onboard battery while passive tags are powered by an external reader's signal. In passive tags, the reader's transmission energizes the tag's antenna, which in turn resonates back a corresponding signal. RFID tags and readers are typically designed to transmit data on a fixed frequency band. Frequency impacts both read rate and distance. Lower frequency tags typically have shorter read distances and slower data transfer rates than higher frequency tags. Passive tags are usually classified depending upon the frequency band in which they operate.
An RFID reader or interrogator retrieves information stored on a tag through a radio frequency signal picked up by the reader's antenna. How this data signal is generated depends on the tag being read. An active reader receives signals broadcast by the tag's internal RF transmitter. Some active tags broadcast their signals continuously without regard to whether there is a reader within receiving range. Other active tags require a prompt signal from a reader before broadcasting their data stream.
A passive reader transmits a signal strong enough to energize the target tag's antenna and circuitry. The tag resonates the signal back to the reader in a slightly modified form that is decoded to extract the data stream. Since they provide the energy for the tag's transmission, passive readers must have a considerably more powerful signal than active readers. An RFID reader is capable of reading multiple tags within its transmission field.
RFID readers come in two basic configurations: mobile and fixed. Mobile readers are usually employed as peripheral devices on handheld or vehicle mounted terminals. Fixed readers may support one or more external antennas. The reader and antenna may also be contained in a single housing.
A challenge faced when using either a fixed reader or a mobile one is orienting the reader and/or the RFID tag such that the RFID is read. For instance, in fixed installations, items associated with tags may need to be oriented such that they face the reader for optimal readability or multiple readers are required. This is especially true if the item is comprised of a liquid or has a metallic container as these materials may attenuate the RF signal used by the RFID tag and reader. Likewise, it may be difficult to orient a mobile reader such that the RFID tag associated with that item is read, especially in high-speed environments experienced in manufacturing and shipping. Another challenge faced in today's manufacturing, shipping and processing environments is quickly and accurately reading an RFID tag without adding an additional delay to the process.
For instance, as described in U.S. Pat. No. 6,335,685 issued to Gabriel et al. on Jan. 1, 2002, items having RFID tags attached thereto are either moved linearly and horizontally in front of a RFID reader with the RFID tags on the items oriented towards the reader or non-moving items are read by activating the RFID tag with a laser device, thus in both instances requiring orientation of the RFID tag toward the laser or toward the reader.
An unsatisfied need therefore exists for quickly and accurately reading RFID transponders associated with items that overcomes the challenges described above and others mentioned herein.